Grease oxidation

ABSTRACT

A significantly improved version of the ASTM D942 Test Method, with apparatus employable to effect the same, is provided. This is useful in measurement of grease oxidation.

This claims the benefits under 35 USC 119(e) of U.S. provisional utilitypatent application Nos. 61/962,464 filed on Nov. 7, 2013 A.D., and61/965,160 filed on Jan. 24, 2014 A. D. The specifications of thoseapplications, including drawings, are incorporated herein by reference.

GENERALIZED OVERVIEW OF ART AND PURVIEW OF THE INVENTION

Grease oxidation resistance has always been an important aspect of itsperformance. Yet, because of its nature as a gelatinous colloidaldispersion in oil, understanding and improving this aspect of greaseperformance continues to be a technical challenge. Moreover, the widerange of components used to formulate this most ancient of blendedlubricants, makes it difficult to devise bench tests that willaccelerate grease response to oxidation conditions without loss ofcorrelation with actual applications. This invention applies acombination of an advanced version of a test method that has been usedfor decades but with virtually no ability to compare greases. Precisecontrol of test temperature and measurement of change in moderately highoxygen pressure is combined with infrared analysis of the grease afterthe test period of 100 hours. The technique has shown significantdifferences among greases common in lubrication. Apparatus is also ofconcern.

BACKGROUND TO THE INVENTION

As the most ancient of lubricants—said to extend back into the laterStone Age of man—grease is nonetheless perhaps the least understood andyet most widely used form of lubrication. This situation is not for wantof effort to more clearly understand its response to operatingconditions but more because of the wide range of those operatingconditions and the range of components that over the millennia have beenfound to make it more usable.

A property having a major effect on the utility of grease is itsresistance to oxidation and the consequences of this resistance on itsability to maintain an effective level of lubrication. Such resistanceto oxidation and degradation under the stresses imposed by hightemperatures and thousands of hours of operation has always been animportant feature of grease performance, and a particular focus of itsuse and development over the years. As a consequence, increasinglyadvanced bench techniques have been developed to improve theunderstanding of both how the oxidation resistance can be enhanced byformulation and how this resistance can be lost in service.

Thus, oxidation stability is a very important property of lubricatinggreases. And so, any bench test capable of measuring this property isimportant to the degree that it is capable of predicting either theshelf-life or the service-life of a grease, or both.

Prior Art Grease Oxidation Test

In the 1940's the desire for a readily applicable bench test for qualitycontrol of a grease formulation by measuring its oxidation resistanceled to the development and publication of ASTM Test Method D942 in1947—a test method which became a standard and continues to be applied.Ref., ASTM Method of Test D942-02, “Oxidative Stability of LubricatingGreases by the Oxygen Pressure Vessel Method” (Reapproved 2007), ASTMVol. 5, pp. 352-356, 2010; IP Method of Test 142/85 (92). It isroutinely used to measure batch-to-batch grease oxidation stability, andalso has been used in screening new grease formulations in development.That test requires exposure of 20 grams of a grease in five glass disheswith an exposed surface area of approximately 25 cm² per dish, thus 125cm² per test. The dishes are stacked with an about 5-mm gap betweenthem. Compare, FIG. 1. The combined stack of grease-filled dishes arethen inserted into a cylindrical pressure chamber and exposed to oxygenof not less than 99.5% purity at an initial pressure of 100 pounds persquare inch (PSI=690 kPa) and room temperature, which is then increasedto 99±0.5° C. Under this increased temperature, the oxygen pressure iscarefully released to maintain no more than 110±2 PSI. The test istypically continued for a chosen period of 100 or 200 hours, withresultant decrease in oxygen pressure as a result of grease oxidationtaken as the test result.

Some Limitations of ASTM D942 as Known in the Prior Art

Despite being relatively simple and straightforward, it is clearlystated in the ASTM D942 method that the test is severely limited inapplication to any other use than quality control of a greaseformulation. For example, it is stated that the test should not beapplied to compare the oxidation stability of the tested grease toactual behavior in service. Similarly, because of differences amonggrease formulations and the effects of oil volatility, comparison ofoxidation resistances of different greases for a given application isalso not recommended. Nor should the test be used to predict thestability of grease stored in containers or the oxidation stability ofgreases used in bearings and motors since only controlled oxidation of aphysically stable surface of grease is used in the test.

Moreover, the ASTM D942 Test Method as known in the prior art is a verytime consuming (100-500 hours) and labor intensive test requiringcomparatively large sized samples. Thus, it is inapplicable to measuringsmall sample sizes taken from operating bearings or other applicationsto determine remaining oxidation resistance.

On the other hand, its simplicity is desirable. Perhaps an improved testmay preserve this.

A SUMMARY OF THE INVENTION

Provided hereby is a significantly improved version of the ASTM D942Test Method, with apparatus employable to effect the same. The same isuseful in measurement of grease oxidation.

Hereby, the art is advanced in kind. The desirable simplicity andstraightforward features of the ASTM D942 Test Method are retained, butits undesirable liquid bath and large sample size requirements areeliminated. Fourier Transform Infra Red (FTIR) analysis can beadvantageously applied to extend the application of the ASTM D942 TestMethod to comparative oxidation responses of greases. The FTIR can beequipped with Attenuated Total Reflectance (ATR). Beyond this,simultaneous analysis of several small grease sample sizes can extendthe productivity of the present bench test and its methodology indetermining grease oxidation resistance, and its utility is not limitedto batch-to-batch uniformity of grease samples. Thus, much greaterefficiency is gained, with reduced sample size as well as simultaneousevaluation of multiple grease samples. Moreover, the level ofinformation obtained from the grease samples is increased, with morein-depth information on grease oxidation, which consequently allowscomparison of the oxidation stability of various types of grease. Rapidscreening using ASTM D942 type test conditions can be used tosignificantly increase the speed of acquiring information on oxidativestability of greases in the development process. A small footprintinstrument is used.

Numerous further advantages attend the invention.

DRAWINGS IN BRIEF

The drawings form part of the specification hereof. With respect to thedrawings, which are not necessarily drawn to scale, the following isbriefly noted:

FIGS. 1-4 b and 15-22 depict apparatus employed herein.

FIGS. 5-14 and 23-30 are graphs depicting results hereof.

ILLUSTRATIVE DETAIL

The invention can be further understood by the detail set forth below.As with the foregoing, the following, all of which may be read in viewof the drawings, is to be understood in an illustrative but notnecessarily limiting sense.

A First Illustration

ASTM D942 Type Tests Using a Bath-Free RPVOT Instrument

At least one of the inventors considered that the physical configurationof the ASTM D942 test and grease oxidation exposure, coupled withsubsequent analyses of the grease by FTIR had considerable merit if someway could be found to eliminate the need for the awkward anddifficult-to-maintain oil bath. Fortunately, such a test instrument wasavailable, and it was adapted.

In the last few years a new approach to meet ASTM Test Method theRotating Pressure Vessel Oxidation Test (RPVOT) D2272, was developed.Ref., ASTM Method of Test D2272-02, “Oxidative Stability of SteamTurbine Oils by Rotating Pressure Vessel” (Reapproved 2011), ASTM Vol.5, pp. 846-864, 2010; T. W. Selby, et al., “Studies of the OxidationDynamics of Turbine Oils—Initial Data from a New Form of the RPVOT,”ASTM Symposium on Oxidation and Testing of Turbine Oils, Dec. 5, 2005,Norfolk, Va. See, patent Nos. U.S. Pat. No. 7,678,328 B1 and U.S. Pat.No. 8,679,405 B1—both incorporated herein by reference. This instrument,called the Quantum®, does not use a liquid bath to heat the pressurechamber. In essence, it is a bath-free isothermal instrument, which wasfirst applied to the RPVOT method and incorporated into D2272 in 2009after extensive round robin testing. Ref., ASTM D2272 Research ReportRR:D02-1666.

A view of this instrument is shown in FIG. 2a as used for the RPVOTtest. The design of the bath-free Quantum instrument also permits accessto the test substance in the pressure chamber during test to extract asmall sample. See, T. W. Selby, “Modern Instrumental Method ofAccurately and Directly Measuring the Useful Life of Turbine Oils,”OilDoc Conference, Feb. 1-3, 2011, Bavaria, Germany. See also, FIG. 2 b.

Configuration of Quantum Instrument for Grease Oxidation Test

It was found that the Quantum instrument—which actually is an isothermalreactor capable of many uses—has all of the necessary geometry, heating,and availability of pressurized oxygen as a test condition. Therefore,it was adapted for running the ASTM D942 grease oxidation test.

Accordingly, a steel insert to reduce the inner volume of the Quantuminstrument's pressure chamber and a vertical rack for the five greasesamples are provided. These are shown in FIG. 3 with one of thegrease-filled dishes. See also, FIG. 2b . To further simplify thisalternative use of the instrument, simple steel shelving was configuredinto a pivotable, cradling framework that permitted the instrument to betipped to a vertical position for use in grease oxidation tests or toset in its normal orientation for RPVOT tests. See, FIGS. 4a and 4b .See also, FIG. 2 b.

In FIG. 4a , the Quantum instrument is set into the rotatable shelf topermit the operator to use it for the RPVOT test or for the greaseoxidation test. In FIG. 4b , the shelf holding the Quantum instrument istipped up to the position in which the pressure chamber within theinstrument is vertical and the steel sleeve and rack ofgrease-containing dishes are installed awaiting sealing the lid andpressuring the closed chamber with oxygen.

Application of ATR Infrared

Infrared (IR) spectroscopy has been used for more than a half-century inthe study of grease oxidation, starting with the work of Rappoport in1952. E.g., O. Z. Pencheva and M. D. Tsonev, “Use of IR Spectroscopy inResearch of Grease Oxidation,” Khimiya Teckhnollogiya Topliv Masel, 7(July, 1973), 55-57; Z. M. Zhang, et al., “InfraRed Refractive Index andExtinction Coefficient of Polyimide Films,” International Journal ofThermophysics, Vol. 19 (1998) 3, 905-915; G. Rappoport, LubricationEngineering, Vol. 8 (1952) 129, 134. The introduction and development ofFTIR spectroscopy was a major development permitting creative comparisonof IR spectra. More recently, the use of ATR IR, particularly ATR FTIR,has further extended the use of IR to materials which are not veryamenable to transmitting IR light through the sample to generatespectra. For greases, with their colloidal, gelatinous, and otherwiseheterogeneous dispersion of components, ATR using only the reflectivesurface of the sample is a desirable comparative source of IR spectra.

Combined Analytical Technique to Compare the Oxidation Resistance ofGreases

A test protocol was developed for 1) first determining the response of agrease to ASTM D942 using oxygen pressure decrease; then 2) sampling thegrease in the dishes from the test; and finally 3) comparing theoxidation resistance of the greases using ATR FTIR spectra.

Results of ASTM D942 Tests of Five Greases Using the Quantum Instrument

Applying the modified Quantum instrument shown in FIGS. 2b , 3, 4 a and4 b, ASTM D942 grease oxidation tests were run for 100 hours andadditionally, in some cases, 200 hours. Samples were not rotated. Foreach test, pressure change with time was continuously recorded.Following each test, the five dishes of grease were sampled for infraredanalysis on an ATR equipped FTIR.

In first tests, it was found that there was essentially no differenceamong individual dishes from the five-dish stack. Consequently, only thetop dish was sampled for subsequent IR analyses.

Grease #1

Tests using the ASTM D942 method were run for both a 100-hour and a200-hour test period under this test method. FIG. 5 shows the closelysimilar pressure traces obtained during these tests. Grease #1 was runat both 100 hours and 200 hours for comparison of both 1) therepeatability of the pressure-decrease curves in the first 100 hours;and 2) the continuing rate of oxidation for the next 100 hours ofexposure.

It is evident that the oxidation curves are quite similar and that ASTMMethod D942 as applied by the modified Quantum instrument is capable ofproviding reproducible information. The oxygen pressure in Test 1 at 100hours was 96 PSI. At 200 hours of test it was 86 PSI.

Grease #2

ASTM D942 tests were conducted in replicate for 100 hours on Grease #2.Results are shown in FIG. 6.

The response to ASTM D942 was quite strong but highly repeatable. Thisgrease may have begun oxidizing even before the chamber temperaturereached its maximum of 99° C. Interestingly, the final pressures in thechamber showed total oxygen uptake during test by dropping toatmospheric pressures of about 15 PSI.

Grease #3

As mentioned earlier, according to the protocol of ASTM Test MethodD942, when the oxygen pressure rises to 110±2 PSI, the oxygen iscarefully released to keep it at this level until oxidation of thegrease begins. FIG. 7 suggests the consequences of not relieving theoxygen pressure in Test 1 for almost 2½ hours.

The data indicate that additional grease oxidation may occur under suchpreliminarily higher oxygen pressure. Final oxygen pressures were 96 PSIafter 100 hours for Test 1 and 91 PSI after 200 hours for Test 2.

Grease #4

Grease #4 was found to be highly resistant to oxidation in the D942 testas shown by the three replicate tests in FIG. 8. In these three tests,the lowest oxygen pressure after a 100-hour test was only 107 PSI.

Grease #5

Evaluation of Grease #5 shown in FIG. 9 indicated this grease to also befairly resistant to oxidation over 100 hours of test.

ATR-FTIR Analyses of Greases Oxidized Hereby

Following exposure of each of the foregoing five greases to the presentmodified type ASTM Method D942 for 100 or more hours, the oxygenpressure is released. When the pressure chamber is sufficiently cooled,the instrument is opened, and the rack of dishes is removed.

About 2-4 milligrams of grease sample was needed in analyzing its FTIRspectrum using the ATR. For consistency in the study, the grease samplewas skimmed from the surface of the grease in the top plate.

ATR-FTIR Analysis of Grease #1

As shown in FIG. 5, Grease #1 was subjected to 100 and 200 hoursoxidation exposure in ASTM Method D942 run in the modified Quantuminstrument.

FIG. 10 shows an analysis of the spectrum of fresh Grease #1 from awavenumber of 1600 to 2200 cm⁻¹. Values of the percent transmittance ofonly the fresh Grease #1 are shown on the left-hand ordinate. On theright-hand ordinate, the FTIR values of percent transmittance for theoxidized grease samples are subtracted from those of the fresh grease(in this case Grease #1). This shows the effects of oxidation on thefresh test grease by the increase in concentration of oxidized greasecomponents and thus a decrease in percent transmittance.

It is evident and confirming that at the wavenumbers betweenapproximately 1700-1750 cm⁻¹ associated with carbonyl oxidation products(carboxylic acids, ketones, aldehydes, etc.) there is, as would beexpected, substantial increase as a consequence of oxidation. Moreover,greater oxidation is shown in the 200-hour test compared to that of 100hours. Interestingly, even in the fresh grease, there are evident peaksshown in the vicinity of 1700-1750 cm⁻¹. This suggests that theformulation of this grease may contain carbonyl additives components orthat the grease may experience some oxidation in formulation.

ATR-FTIR Analysis of Grease #2

As discussed in Section 3.2 and shown in FIG. 6, Grease #2 was veryoxidation susceptible in the ASTM D942 oxidation test protocol. Thethree curves shown in FIG. 11 resulted after the grease was tested twiceand the resulting FTIR spectra subtracted from that of the fresh Grease#2. The peaks of Test 1 and Test 2 are both at 1710 cm⁻¹ with reducedpercent transmittance of 17% and 11%, respectively, at this wavenumberclosely associated with hydrocarbon oxidation.

ATR-FTIR Analysis of Grease #3

Grease #3 demonstrated oxidation susceptibility in FIG. 7. In this, itis similar to Grease #1. As shown in FIG. 12, however, when the FTIRspectra were obtained, the degree of oxidation shown by the decrease inpercent transmission was somewhat greater than Grease #1.

ATR-FTIR Analysis of Grease #4

As expected from FIG. 8, in FIG. 13 Grease #4 shows high oxidationresistance. The three tests run at 100 hours show some variability inthe oxidation wavenumber region indicating a sensitive antioxidant.

ATR-FTIR Analysis of Grease #5

From the ASTM D942 oxidation tests, Grease #5 also seems resistant tooxidation. This becomes clear in FIG. 14. Essentially, no oxidation isshown by Grease #5. Moreover, in some distinction to Grease #4, the fourtests on Grease #5 are fairly similar.

Discussion

As virtually the most ancient form of man-made lubricant, grease hasbeen unique in its complex forms and the nature of its tribologicalcontributions. Grease is subject to many forms of stress in providinglubrication. One of the more important of these is oxidation. This isparticularly the case since, in many applications, the grease is veryexposed to the environment composing and surrounding the lubricationsite—however varied that environment may be. Moreover, unlike forms ofliquid lubrication, there is seldom much that can be done to some degreeto protect the grease from its often harsh environment. As a consequenceof the complex chemistry and composition of greases, and the variablenature of the environment in which given grease is applied, standardbench tests of the chemical performance of greases such as ASTM D942 areinfrequent. This is in contrast to the more commonly employed physicalbench tests for wear and physical degradation in service. It was forthis reason that the application of ASTM D942 was chosen for improvingits instrumental simplicity and heating control and removing its statedinterpretive limitations mentioned above.

Results of this illustration showed clearly that among the five greasesstudies, the combination of ASTM Method D942 and the subsequent FTIRanalysis of the spectra of the original grease compared to the greaseafter oxidation showed that the FTIR information supported therelatively simplistic information of ASTM D942 alone. Moreover, thelimitations of ASTM D942 when used alone were overcome with the sharperinformation provided by the FTIR analysis.

Some Conclusions

On the basis of the foregoing, it would seem reasonable that the ASTMMethod D942 should be extended to include the use of FTIR analysis. Withsuch information the ASTM Method could be used to show correlation withfield experience and to also permit selection of better additives forspecific applications. The use of the FTIR spectrum subtractiontechnique shown herein was helpful in more clearly discriminating thechanges in different greases brought about by oxidation.

A Second Illustration

Use of FTIR

As above, a modern FTIR instrument was equipped with ATR. Thereby, atechnique for oxidation measurement that combines the ASTM D942 testwith FTIR analysis overcomes the limitations of the original ASTM D942test. The combination of FTIR with ASTM D942, referred to in thisillustration as the Advanced Technique, would provide much more in-depthinformation on grease oxidation which would consequently allowcomparison of the oxidation stability of various types of grease.

It was found initially that sufficient information could be obtainedfrom IR of the surface of the grease samples. This led to theconsideration of using much smaller grease sample in the pans and, thus,the ability of applying the principles of ASTM D942 and FTIR to sampleshaving the same surface area in the test, but much less grease mass.This approach would not produce the same oxygen pressure decrease, butthe FTIR oxidation information would be the same.

This led to an additional test concept in which it was considered thatrapid screening of grease or additive formulations based on oxidationresistance should be possible. The screening technique uses the ASTMD942 test conditions to oxidize grease; however, IR analysis is usedprimarily to measure oxidation resistance of the sample. This method canbe used to significantly increase the speed of acquiring information onoxidative stability of greases under development.

Grease Oxidation Measurement Techniques

This second illustration builds upon the first illustration. Thatillustration compared the oxidation resistance of several greases ofvarying oxidation resistance.

As before, the experimentation of this illustration was carried out in aspecially modified iso-thermal reactor normally used in determiningoxidation resistance of liquid lubricants per ASTM D2272. FIGS. 2a and4b show the instrument before and after a modification that permits theinstrument to be used alternatively in either test configuration. Anadvantage of modifying the iso-thermal reactor to conduct the ASTM D942test was that it did not require the care and concerns of a liquid bathas the sample chamber is heated by electrical resistance. A stainlesssteel insert, e.g., FIGS. 2b , 3, 15, was used to obtain the appropriatechamber volume for ASTM D942 testing. Other accessories, including asample rack and sample pans were provided to comply with the method, andare shown in FIG. 3. The same test setup was utilized in the presentillustration.

Application of the modified iso-thermal reactor for the ASTM D942 methodwas validated in the first illustration by testing multiple greasesamples for 100 and 200 hours. Samples were not rotated. Consistentresults were obtained from repeat tests and show good agreement withASTM D942 tests run at an external laboratory with standard testequipment. All results were within the method's repeatability andreproducibility.

Again, according to the ASTM D942 Test Method, 20 g of a grease sampleis tested in five glass dishes with an exposed surface area ofapproximately 25 cm² per dish and a total surface area of 125 cm² pertest. The dishes are stacked with a gap of approximately 5 mm betweenthem. The combined stack of grease-filled dishes are then inserted intoa cylindrical pressure chamber and exposed to oxygen of not less than99.5% purity at an initial pressure of 100 pounds per square inch (PSI)and room temperature which is then increased to 99±0.5° C. Under theincreased temperature, the oxygen pressure is maintained at 110±2 PSI.The test is continued for a chosen period of time and decrease in oxygenpressure resulting from grease oxidation is reported in PSI as the testresult.

Five lithium based greases of varying oxidation resistance were chosenfor the current work. Greases 1, 2 and 3 are developmental greasesprovided by Loadmaster Lubricants LLC, interested in extending theinformation gained from ASTM D942. Greases 1, 2 and 3, respectively, aresaid to be high load-carrying lithium grease, fully synthetic lithiumcomplex grease and high load carrying lithium complex grease. Greases 4and 5 are commercial lithium-complex greases and the compositions areproprietary.

Advanced Technique for Oxidation Measurement

Again, IR spectroscopy has been used for over half a century in thestudy of grease oxidation. E.g., G. Rappoport, Lubrication Engineering,vol. 8 (1952); O. Z. Pencheva et al., “Use of IR Spectroscopy inResearch of Grease Oxidation,” Khimiya Teckhnollogiya Topliv i Masel,Vol. 7 (July, 1973); Z. M. Zhang, et al., “Infrared Refractive Index andExtinction Coefficient of Polyimide Films,” International Journal ofThermophysics, Vol. 19 (1998); P. M. Cann, et al., “Grease Degradationin ROF Bearing Tests,” Tribology Transactions, Vol. 50 (2007); S. Hurleyet al., “Infrared Spectroscopic Characterization of Grease LubricantFilms on Metal Surfaces,” NLGI Spokesman, Vol. 64 (October, 2000). Thelevel of oxidation in petroleum-based lubricants in general is measuredin the carbonyl region (1670 to 1800 cm-1). IR energy is absorbed inthis region as a result of the carbonyl group (C═O) stretch from variouscarbonyl compounds including, ketones, esters, carboxylic acids,carbonates, aldehydes, anhydrides and amides. The FTIR peak around 1715cm⁻¹, generally known as the “oxidation peak,” results from CO=stretchand indicates breakdown of the lubricant and formation of oxidationby-products.

Combining the ASTM D942 method with IR analysis is a dependable approachto grease oxidation measurement. The following steps were used in thetechnique:

-   1) Response of a grease to ASTM D942 is determined by measuring    change in oxygen pressure in 100 hours.-   2) The grease is sampled from the pans after the test.-   3) Oxidation resistance of the grease is analyzed using ATR-FTIR    spectroscopy.

For this illustration a PerkinElmer Spectrum 100 FTIR Spectrometerequipped with a universal ATR sampling accessory was employed. Thelatter was indispensable in applying IR to opaque materials by using thereflection from the sample surface. IR analysis was conducted using anabout 2-4 mg sample. Multiple IR spectra taken from the same sampleshowed no measurable difference in the resulting spectra, whichindicated that effects of the small variation in sample size isnegligible. Sample was skimmed from the surface of the grease.

Screening Technique

Attempts have been made in the past to design a simple and rapidscreening test based on grease oxidation stability that correlates wellwith in-service oxidation conditions. Ref., W. W. Bailey et al.,“Dynamic Oxidation Stability of Lubricating Greases,” NLGI Spokesman,Vol. 15 (April, 1982). In this illustration, a test concept has beendeveloped for rapid screening of grease samples based on oxidationresistance. The concept is similar to the High Throughput Screening(HTS) technique used in drug discovery.

In the HTS process for drug discovery, biological targets are identifiedand potential compounds are screened against the target. This wasoriginally an expensive, tedious, and time-consuming manual process,which has been termed Low Throughput Screening (LTS), which usually tookmonths. Over the last two decades, innovations in technology transformedthe LTS into an automated microprocessor controlled robotic process,i.e., HTS. This quantitative step makes it possible to screen10,000-100,000 compounds within 24 hours.

A Screening Technique similar to HTS may be useful to speed up thegrease development process. As the ASTM D942 Method requires five samplepans, it was considered that a possibility that five different greasesin the same test could be evaluated. The screening technique does notneed to be limited to five grease samples. Initially, five greases werechosen mainly because the current ASTM D942 Test Method setup isequipped with five sample pans. The setup can be easily modified to testany reasonable number of greases at the same time, as an illustration,say, from one to about twenty, to include about from two or three to tenor fifteen, and about from four to seven or eight.

The screening test concept was evaluated in the following two steps.

Step 1: Reduced Sample ASTM D942 Type Test

A modified ASTM D942 test with smaller sample amounts was evaluatedusing Grease 2. Four and five grams of Grease 2 were tested in thefollowing two configurations:

-   1) 5 g, 5-Pan Test: five pans, each containing 1 g of Grease 2, were    tested in the iso-thermal reactor for 100 hours following the D942    test conditions (99° C. and 110-PSI initial pressure).-   2) 4 g, 1-Pan Test: one sample pan, containing 4 g of Grease 2, was    tested in the same way.

Grease 2 was spread out in each pan, and the surface was leveled using aclean spatula to minimize the impact of any differences in surface areabetween pans. Following the 4 g, 1-Pan and 5 g, 5-Pan Tests, 2-4 mg ofGrease 2 was sampled for IR analysis.

Step 2: HTS Test

Next, a screening test concept was developed where five differentgreases were oxidized simultaneously under ASTM D942 type testconditions, and then oxidation resistance of the greases was measured byIR analysis. The screening technique uses the Quantum test equipment tooxidize the grease samples; oxidation, however, is measured primarily byIR analysis. The following two configurations were evaluated:

-   1) 5 grease-5 pan @1 g: 1 g each of the 5 grease samples was tested    in the iso-thermal reactor for 100 hours at the D942 test conditions    (99° C. and 110-PSI initial pressure).-   2) 5 grease-5 pan @4 g: 4 g each of the 5 greases was tested in the    same way.

The grease samples were spread out in the pans, and the surfaces wereleveled using a clean spatula to minimize the impact of any differencesin surface area between the pans.

As would be expected, oxygen uptake during the 5 grease tests does notcorrelate with the oxidation stability of the individual grease samples.The 5 grease screening test disregards the change in pressure generatedby the oxidation process and utilizes IR analysis to assess the extentof oxidation of the grease samples.

Results

Results obtained are set forth below.

Standard ASTM D942 Type Test

Utilizing the Quantum iso-thermal reactor, each of the five greases wassubjected to 100 hours of the standard D942 Test conditions.

FIG. 23 shows overlay of pressure vs. time plots for Greases 1, 2 and 3.Greases 1 and 3 show relatively small changes in pressure in 100 hourscompared to Grease 2. The results indicate that Greases 1 and 3 arerelatively resistant to oxidation. In contrast, Grease 2 appears to behighly susceptible to oxidation as the chamber pressure reduced toatmospheric level of about 15 PSI as a result of complete oxygen uptakeduring the 100-hour ASTM D942 test.

FIG. 24 shows the responses of Greases 4 and 5 to 100-hour ASTM D942tests. A very small change in pressure was observed for both of thegreases indicating that these greases are highly resistant to oxidation.Table 1 below compares the changes in oxygen pressure for all fivegrease samples during the ASTM D942 type tests.

TABLE 1 100-hour ASTM D942 Oxidation Grease 1 Grease 2 Grease 3 Grease 4Grease 5 Pressure 14.4 95.0 13.5 6.0 2.8 Drop (PSI)Advanced Technique

In the advanced technique, the grease samples oxidized by 100-hour ASTMD942 type test were analyzed by FTIR-ATR. Initially, each of the fivedishes of grease from the ASTM D942 type test was sampled for IRanalysis. No significant differences were observed between the dishesfrom the five-dish rack. In subsequent tests, only the top dish wassampled for IR analysis.

The IR peak around 1715 cm¹, known as the “oxidation peak,” wasevaluated to measure the extent of oxidation in the five greasesfollowing individual 100-hour D942 tests. FIG. 25 compares the ATR-FTIRspectra from Greases 1, 2 and 3 following oxidation by 100-hour ASTMD942 type tests. Intensity of the oxidation peak is higher for all threegreases after the ASTM D942 tests compared to the fresh grease samples.The IR analysis clearly indicates oxidation of the grease samples; thelevel of oxidation, however, is substantial for Grease 2 compared to theother two greases. As observed previously in FIG. 24, the change inoxygen pressure for Grease 2 during the 100-hour ASTM D942 type test wasalso much higher compared to Greases 1 and 3. FIG. 26 compares IRspectra of fresh and oxidized Greases 4 and 5. No oxidation peak isobserved in either grease before or after the 100-hour ASTM D942 typetest. As discussed above, both of these greases produced very littlechange in pressure during the 100-hour ASTM D942 type tests.

Therefore, IR analysis agrees well with ASTM D942 type test results,which confirms that Grease 2 is highly susceptible to oxidation, Greases1 and 3 are moderately stable, and Greases 4 and 5 are extremelyresistant to oxidation under similar oxidative conditions.

The results also support the approach of using IR analysis as analternate way to measure grease oxidation stability. The combination ofASTM D942 test method and the subsequent FTIR analysis evidentlyenhances the relatively simplistic information provided by ASTM D942test alone. Moreover, the limitations of ASTM D942 test when used aloneare overcome with the more in-depth information provided by infraredanalysis.

Reduced Sample-D942 Type Tests

FIG. 27 shows a comparison of the responses of Grease 2 to ASTM D942type, 4-g, 1-Pan and 5-g, 5-Pan tests, where each test was conducted for100 hours. Five grams of Grease 2 distributed in five sample pans wereevaluated in the 5-g, 5-Pan test whereas only one sample pan containing4 g of Grease 2 was evaluated in the 4-g, 1-Pan test. As observed inFIG. 27, an ASTM D942 type procedure produces a pressure loss of 95 PSIfor this grease, which is significantly higher compared to 56.9 and 32.7PSI obtained during the 4-g, 1-Pan and 5-g, 5-Pan tests, respectively.

The results clearly indicate a correlation between the change inpressure during these tests with the volume of oxygen available per massof sample grease. Table 2 compares the results of the ASTM D942 typetest with 4-g, 1-Pan and 5-g, 5-Pan tests on Grease 2.

TABLE 2 100-hour Oxidation of Grease 2 Standard type 5 g, 4 g, D9425-Pan 1-Pan Pressure 95.0 56.9 32.7 Drop (PSI)

FTIR spectra taken from Grease 2 following the standard type ASTM D942and the 4-g, 1-Pan and 5-g, 5-Pan tests are compared in FIG. 28. Themodified tests with reduced sample mass caused a higher level ofoxidation in Grease 2 compared to the standard type ASTM D942 test. IRanalysis clearly shows that the standard type ASTM D942 test does notcompletely oxidize Grease 2 during the 100 hours.

It is apparent in these results that the standard type ASTM D942 testleaves Grease 2 partially oxidized, which is caused by completeexhaustion of oxygen in the reaction chamber before the test ends,whereas the reduced sample tests allow further oxidation of the grease.The ratio of oxygen volume in the chamber to the sample mass is higherin case of the latter.

Incomplete information is likely obtained from the standard type ASTMD942 test for greases that are highly susceptible to oxidation. Theresults demonstrate another limitation of the ASTM D942 method, as wellas the significance of coupling the test with IR analysis.

Screening Test

As discussed above, there was considerable agreement between the testresults obtained by the standard type ASTM D942 test and the AdvancedTechnique. In an effort to develop a Screening Test concept, the fivegreases were tested simultaneously in the following two configurations:5-grease, 5-pan Test (@1 g) and a 5-grease, 5-pan Test (@4 g).

FIG. 29 compares the effect of oxidation on Grease 2 for the standardtype ASTM D942 test, 5-grease, 5-pan (@1 g) and 5-grease, 5-pan (@4 g)screening tests where each test was conducted for 100 hours. Thescreening tests clearly obtained a higher level of oxidation of thissample compared to the standard ASTM D942 type test, as measured by IRanalysis. Both the standard type ASTM D942 test and the screening testsfound Grease 2 to be highly susceptible to oxidation compared to theother four greases.

As observed in FIG. 30, IR analysis detected no oxidation of Grease 4after the standard type ASTM D942 test; a minimal level of oxidation,however, was measured in the same grease after the Screening Tests. Bothtests indicated that Grease 4 is highly resistant to oxidation. Theresults imply that the 5-grease test creates a relatively harshoxidative environment compared to the standard type test, which isdesigned to measure oxidation of a single grease sample.

The preliminary results obtained in this illustration demonstrate thatthe screening test concept can be useful in rapid selection of grease oradditive formulations. This approach could significantly reduce the timeneeded for grease research and development.

Some Conclusions

ASTM D942 is severely limited in its applications to any other use thanquality control in grease manufacturing processes. The goal of thisillustration was to improve the ASTM D942 Test Method, by combiningprecise control of test temperature and measurement of oxygen pressurewith IR analysis, and that goal was met. The in-depth informationprovided by FTIR analysis expands the applications of the originalmethod. The extended test is capable of comparing oxidation stability ofvarious types of grease. Based on this analysis, the ASTM D942 testshould be extended to include the use of IR analysis.

In addition, a screening test concept was developed. This involvedsimultaneous oxidation of multiple grease samples under ASTM D942conditions and measurement of oxidation resistance by IR analysis. Theresults indicated that the screening test and the standard ASTM D942Test Method measure comparable oxidation tendency of the grease samples.The screening test can be useful in selecting preliminary formulationsin the grease development process by significantly shortening theanalysis time.

Pivotable, Cradling Framework, and Accessories

The pivotable, cradling framework can hold the bath-free, isothermal,bomb instrument, especially embodied as a Quantum instrument, which isan embodiment of a rotatable bomb as of the incorporated patents, Nos.U.S. Pat. No. 7,678,328 B1 and U.S. Pat. No. 8,679,405 B1. It can permitthe cylindrical chamber of the rotatable bomb instrument to be tipped toa vertical position with respect to its cylindrical chamber axis from anorientation in which the cylindrical chamber is acutely angled withrespect to a supporting surface such as a bench top when the rotatablebomb instrument has its bottom parallel with the bench top. Compare FIG.2a with FIGS. 2b, 4a and 4b . See also, FIGS. 21 and 22. Further, thepivotable, cradling framework and other accessories can have suchfeatures as found in FIGS. 15-22, as follows:

FIG. 15 depicts four views of a grease vessel insert, i.e., a hollow,annular type, cylindrical insert, which also may be known as a volumereducer, for the cylindrical chamber of the rotatable bomb instrument.It can be made, for example, of #304 stainless steel with a #62 surfacefinish. Other materials may be employed.

FIG. 16 is a side view of a volume reducer lifting handle, for example,to lift the grease vessel insert. It can be made, for example, of a0.110-inch stainless steel spring wire. Another size or material may beemployed.

FIG. 17 depicts two further views of a dish holder assembly forvertically stacking dishes, which may also be known as pans, for holdingup to five grease samples, for example, one sample per dish. Such anassembly may be configured to hold more or less dishes, as alluded toabove.

FIG. 18 depicts two views of a dish holder stand shelf that may be foundin the assembly of FIG. 17. It is made, for example, of #304 stainlesssteel with a #62 surface finish. Another material may be employed.

FIG. 19 depicts two views of a dish holder stand shelf that may be foundin the assembly of FIG. 17. It is made, for example, of #304 stainlesssteel with a #62 surface finish. Another material may be employed.

FIG. 20 depicts three views of a lifting tab for a dish holder standthat may be found in the assembly of FIG. 17. It is made, for example,of 0.025-inch #304 stainless steel with a #62 surface finish. Anothersize or material may be employed.

FIG. 21 depicts two views of a side of a stand, i.e., the pivotable,cradling framework, for a grease oxidation device hereof, for example,the Quantum instrument. It is made of “UNOBTANIUM” material and has a#62 surface finish.

FIG. 22 depicts a number of views of a stand, i.e., the pivotable,cradling framework, for a grease oxidation device hereof, for example,the Quantum instrument, of which sides are found in FIG. 21. It is madeof “UNOBTANIUM” material and has a #62 surface finish.

FURTHER DISCLOSURE

Although operating conditions of the ASTM D942 Test Method arebeneficially employed, other conditions may be employed such asdiffering pressures, temperatures, or times. Also, a gas or gas-mixturemay be supplied for operations in addition to or in lieu of oxygen orair to, or gas may be evacuated from, the instrument while it issupplied with at least one dish having a grease sample. The gas orgas-mixture may be substantially inert to or reactive with the greasesample, which, of course would include one or more component(s) makingup the grease sample.

CONCLUSION TO THE INVENTION

The present invention is thus provided. Various feature(s), part(s),step(s), subcombination(s) and/or combination(s) can be employed with orwithout reference to other feature(s), part(s), step(s),subcombination(s) and/or combination(s) in the practice of theinvention, and numerous and sundry adaptations can be effected withinits spirit, the literal claim scope of which is particularly pointed outby the following claims:

What is claimed is:
 1. A method for testing at least one greaseformulation through employment of a bath-free, isothermal bombinstrument, which has a hollow interior, and of an infraredspectrophotometer, the method comprising carrying out the followingsteps (A-G), which are not required to be carried out in series unlessindicated otherwise: (A) providing said bomb instrument, and the atleast one grease formulation, wherein said bomb instrument is arotatable bomb instrument held in a pivotable framework; (B) providingat least one dish, wherein, during operation of said bomb instrument,the at least one dish contains a sample of the at least one greaseformulation; (C) providing the at least one sample of the at least onegrease formulation to the at least one dish; (D) providing the infraredspectrophotometer, wherein the infrared spectrophotometer is an FTIR-ATRdevice; (E) supplying the hollow interior of said bomb instrument withthe at least one dish provided with the at least one sample of the atleast one grease formulation; (F) operating said bomb instrument for apredetermined time under conditions of predetermined heat and pressure,and supplying gas to the hollow interior of said bomb instrument,evacuating gas from the hollow interior of said bomb instrument, orleaving ambient gas in the hollow interior of said bomb instrument,while the hollow interior of said bomb instrument is supplied with theat least one dish provided with the at least one sample of the at leastone grease formulation; and then (G) operating the FTIR-ATR device toprovide infrared spectral information concerning composition of the atleast one sample of the at least one grease formulation.
 2. The methodof claim 1, wherein the gas of step F is gaseous oxygen, which issupplied under pressure to the hollow interior of said bomb instrument;an analytical device that measures change of pressure of the gaseousoxygen in the hollow interior of said bomb instrument is also provided,and is operated as part of step F to measure any change of pressure ofthe gaseous oxygen in the hollow interior of said bomb instrument; andoperating conditions of the predetermined heat and pressure in step Fare an initial heat of room temperature, with a gas pressure of 100 PSI;and a subsequent increase in temperature to 99° C., plus or minus 0.5°C., with maintenance of the gas pressure at no more than 110 PSI, plusor minus 2 PSI.
 3. The method of claim 1, wherein an analytical devicethat measures change of gas pressure in the hollow interior of said bombinstrument is also provided, and is operated as part of step F tomeasure any change in gas pressure in the hollow interior of said bombinstrument.
 4. The method of claim 1, wherein the gas includes gaseousoxygen.
 5. The method of claim 1, wherein the gas does not includegaseous oxygen.
 6. The method of claim 1, wherein said rotatable bombinstrument has a bottom and a cylindrical chamber about a chamber axisset at an acute angle with respect to the bottom; the pivotableframework is a pivotable, cradling framework that permits thecylindrical chamber of the rotatable bomb instrument to be tipped to avertical position with respect to the chamber axis; and is held in thevertical position with respect to the chamber axis; a hollow, annulartype, cylindrical insert is inserted in the cylindrical chamber; and agrease rack holding a plurality of dishes as the at least one dish forcontaining a grease sample, in a vertically stacked configuration, isinserted in the insert.
 7. A method for testing at least one greaseformulation through employment of a bath-free, isothermal bombinstrument, which has a hollow interior, and of an infraredspectrophotometer, the method comprising carrying out the followingsteps (A-G), which are not required to be carried out in series unlessindicated otherwise: (A) providing said bomb instrument, and the atleast one grease formulation, wherein said bomb instrument is arotatable bomb instrument held in a pivotable framework; (B) providingat least one sample dish, wherein, during operation of said bombinstrument, the at least one sample dish contains a sample of the atleast one grease formulation; (C) providing the at least one sample ofthe at least one grease formulation to the at least one sample dish,wherein all of the at least one sample of the at least one greaseformulation is apportioned into the at least one sample dish, with about1 g of the at least one sample of the at least one grease formulationapportioned into each separate dish; (D) providing the infraredspectrophotometer, wherein the infrared spectrophotometer is an FTIR-ATRdevice; (E) supplying the hollow interior of said bomb instrument withthe at least one sample dish provided with the at least one sample ofthe at least one grease formulation; (F) operating said bomb instrumentfor a predetermined time under conditions of predetermined heat andpressure, and supplying gas to the hollow interior of said bombinstrument, evacuating gas from the hollow interior of said bombinstrument, or leaving ambient gas in the hollow interior of said bombinstrument, while the hollow interior of said bomb instrument issupplied with the at least one sample dish provided with the at leastone sample of the at least one grease formulation; and then (G)operating the infrared spectrophotometer to provide infrared spectralinformation concerning composition of the at least one sample of the atleast one grease formulation; wherein the at least one sample of the atleast one grease formulation provided in steps B and C, supplied understep E, operated upon under step F, and at least some of which isoperated upon in step G has parameters selected from the following group(A′, B′): (A′) the at least one sample of the at least one greaseformulation comprises the same grease formulation in each separate dish;and (B′) the at least one grease formulation comprises a plurality ofdiffering grease formulations, with at least one sample corresponding toeach differing grease formulation and hence a plurality of samplesdiffering in formulation from one another on account whereof, with theplurality of samples differing from one another apportioned into aplurality of separate dishes as the at least one dish.
 8. The method ofclaim 7, wherein the parameter A′ applies.
 9. The method of claim 8,wherein there are four or five 1-g samples.
 10. The method of claim 7,wherein the parameter B′ applies.
 11. The method of claim 10, whereinthere are four or five 1-g samples.
 12. The method of claim 7, whereinsaid bomb instrument has a bottom and a cylindrical chamber about achamber axis that is set at an acute angle with respect to the bottom;the pivotable framework is a pivotable, cradling framework that permitsthe cylindrical chamber of the rotatable bomb instrument to be tipped toa vertical position with respect to the chamber axis; and said bombinstrument is held in the vertical position with respect to the chamberaxis.
 13. The method of claim 12, wherein a hollow, annular type,cylindrical insert is inserted in the cylindrical chamber, and a greaserack holding a plurality of dishes as the at least one dish forcontaining a grease sample, in a vertically stacked configuration, isinserted in the insert.